134 Studies in Geology, No. 3 



similar. Lncina orcgonensis Dickerson/*'' from the Tejon 

 Eocene, has more regular concentric sculpture, and is pro- 

 portionally lower. Phacoidcs inuircnsis Dickerson,^**^ from 

 the Martinez Eocene, is closer than oregonensis, but is 

 thicker marginally, has the ventral margin more broadly 

 rounded, and has a posterior sulcus. 



Knowledge of the interior of the shell and the availability 

 of a larger amount of material for study may change the 

 validity of many of these observations, and the author hesi- 

 tated on account of the lack of such evidence to name a 

 species so closely related to other forms as new ; but with 

 these relationships and the possibilities of identity pointed 

 out, future work will probably be made less intricate by 

 the separation of the form instead of including it in a 

 synonymy from which it might necessarily be extricated 

 later. 



Lower Zorritos. Ridge between Ouebradas Heath and 

 Charan. 



Superfamily Cardiacea 



Family CARDIIDAE 



Genus Cardium (Linnaeus) Lamarck 



Subgenus Trachycardium Morch 



Cardium (Trachycardium) corritcnsis n. sp. 



Plate VII — Fig. 12. 



Shell thin, inflated, subequilateral. Anterior margin 

 rounded, not produced ; ventral margin rounded ; posterior 

 margin slightly produced. Umbones high, inflated, narrow. 

 Surface generally convex except on either side of the beaks, 

 where a slight concavity leads into the poorly defined areas. 

 Sculpture of 32 smooth A-shaped ribs w^ith V-shaped inter- 



"■"'Univ. Cal. Bull. GeoL, vol. 9, p. 484, pi. 37, figs. la, b, 1916. 

 "Mdem., vol. 8, p. 132, pi. 10, figs, iia, b. 1914. 



